1. Field of the Invention
The present invention relates to an apparatus to optically modulate light having a plurality of frequency bands corresponding to each modulation signals using a single optical modulator.
2. Description of the Prior Art
Wavelength multiplexing systems are being used to increase capacity in the area of optical fiber communications. As shown in FIG. 10, a wavelength multiplexing system needs to have a light source and an optical modulator for each wavelength, which makes the transmission section complicated.
Proposals for making the light source simple include that disclosed in JP-A 2002-2309, which describes a multiple-wavelength light source that produces multiple-wavelength components simultaneously. However, the optical modulator still needs the number of wavelength multiplexed channels.
Japanese Unexamined Patent Application Publication 2002-318374 discloses a multiple-wavelength optical modulation apparatus, which is shown in FIG. 11. The apparatus uses a Wavelength-Division-Multiplexing mux-demux component to split an incoming optical signal into optical carrier wave signals, and has optical intensity modulators corresponding to the number of carrier waves, and an equal number of optical reflectors. In this case too, the use of numerous intensity modulators makes the apparatus configuration complex.
A paper (“Generation and application of wide-span optical frequency combs,” Korogi, Otsu, JSAP Vol. 67 No. 5, pp. 551-554 (1998)) describes a wide-span optical frequency comb generator using an optical modulator, but this is for one wavelength, and therefore differs from the present invention.
An object of this invention is to provide an apparatus for using modulation signals to optically modulate light having a plurality of frequency bands by respective modulation signals, using a single optical modulator.